The present invention relates to a structure of a semiconductor device for flip chip bonding and a method for producing the semiconductor device.
Most of semiconductor devices have a multi-layer structure in which electrically insulating layers are disposed between the respective layers. Each of the electrically insulating layers has one or more opening portions. There exists wiring for connecting a terminal on a lower side of the electrically insulating layer to a terminal on an upper side of the electrically insulating layer through the opening portion in each insulating layer.
The following method is used for forming such an electrically insulating layer. That is, an opening portion is formed in an electrically insulating layer by the steps of: applying a photosensitive electrically insulating material onto a semiconductor device by a spin coating method; and performing exposure and development thereon. Metal wiring for connecting a terminal on a lower side of the electrically insulating layer to a terminal on an upper side of the electrically insulating layer is formed by the steps of: applying a second photosensitive material onto a layer on the upper side of the electrically insulating layer; performing exposure and development thereon to form a mask; and carrying out a process such as plating, sputtering, CVD, evaporation, etc. The photosensitive electrically insulating material used by a mask is removed after it becomes no longer necessary.
Wiring for connecting a terminal on the lower side of the electrically insulating layer to a terminal on the upper side of the electrically insulating layer can be formed by the aforementioned steps. FIG. 31 is a sectional view showing a part of the semiconductor device formed by the aforementioned steps. In FIG. 31, an aluminum pad 7 is a terminal on a lower side of an electrically insulating layer 12, and a bump pad 3 is a terminal on an upper side of the electrically insulating layer 12. The electrically insulating layer 12 which is formed on a wafer 9 having a semiconductor formed thereon has an opening portion formed over the aluminum pad 7. Metal wiring 11 is formed in an area from the aluminum pad 7 to the bump pad 3 above the electrically insulating layer 12. A bump 10 is formed on the bump pad 3. Incidentally, the formation of wiring in an area from the aluminum pad 7 to the bump pad 3 is termed xe2x80x9credistributionxe2x80x9d. In this illustration, the thickness of the electrically insulating layer 12 is selected to be approximately equal to the thickness of the metal wiring 11.
Flip chip bonding may be a model of method of mounting and bonding a semiconductor device, which is produced in the aforementioned steps, onto a circuit substrate such as a printed wiring board. FIG. 32 is a sectional view of a flip chip-bonded semiconductor device. The bump 10 provided on a terminal of the semiconductor device 13 is once melted and then solidified again on the circuit substrate 14 to thereby bond the semiconductor device 13 onto the circuit substrate 14. A gap between the semiconductor device 13 and the circuit substrate 14 is filled with a highly rigid resin. Incidentally, the resin is termed xe2x80x9cunderfill 15xe2x80x9d and effects reinforcement of the junction portion. JP-A-11-111768 discloses an example of flip chip bonding by use of the underfill.
The aforementioned conventional art, however, has the following problems.
Firstly, there is difficulty in the method of supplying the resin to the gap between the semiconductor device and the circuit substrate. That is, a method using a capillary phenomenon is employed as the method of supplying the resin to the gap that is not larger than 0.3 mm generally. The resin as a material for the underfill is, however, a liquid resin with a high viscosity. Hence, there are problems that a great deal of time is required for filling the gap with the resin and that air bubbles often remain in the resin, etc.
Secondly, there is difficulty in detachment of the semiconductor device. That is, in case that the semiconductor device is to be detached from the circuit substrate for the reason that the semiconductor device bonded onto the circuit substrate is defective, the cured underfill material still remains on the circuit substrate even after the detachment of the semiconductor device. Hence, there is a problem to recycle the circuit substrate.
To solve the first and second problems, it is preferable that the semiconductor device is bonded onto the circuit substrate without application of the underfill. However, if the underfill is not applied, there will arise another problem that the junction lifetime of the semiconductor device is shortened extremely. This is because the underfill is applied for the purpose of preventing the junction portion from being destroyed owing to strain caused by heat generation in the junction portion at use of a finished electric appliance.
Incidentally, when a thick-film electrically insulating layer is formed by printing in order to provide a semiconductor device in which flip chip bonding can be performed without any underfill, there exists a gap corresponding to the thickness of the thick-film electrically insulating layer between the external connection terminal and the bump pad formed on the thick-film electrically insulating layer.
Hence, if an exposure is performed by an ordinary method, insufficiency of resolution arises from being out of focus.
A first object of the present invention is to provide a semiconductor device in which flip chip bonding can be performed without any underfill and a wiring can be formed with high accuracy.
A second object of the present invention is to provide a semiconductor device in which flip chip bonding can be performed without any underfill and in which reliability is improved in the mounting of the semiconductor device on a substrate, or the like.
To achieve the foregoing objects, the present invention is made as described in the appended claims. The first object is achieved by a formation of wiring on a desired electrically insulating layer (thick-film electrically insulating layer) in the aforementioned manner. For example, the line width of wiring on a flat portion of the thick-film electrically insulating layer is made different from the line width of wiring on an inclined portion of the thick-film electrically insulating layer, that is, the line width of wiring on the inclined portion is made large so that the wiring is formed with high accuracy.
If a liquid resist is used, resolution is lowered because the film thickness of the resist is thick in the boundary between the thick-film electrically insulating layer and an electrically insulating layer formed under the thick-film electrically insulating layer. Therefore, a resist of film form is used for forming the wiring with high accuracy.
If, for example, the thickness of the peripheral portion of the thick-film electrically insulating layer is adjusted to be small by adjusting the mask printing condition in order to elongate the lifetime of bonding of the semiconductor device, vertices of bumps located in a corresponding region of the semiconductor device are retreated towards the semiconductor device side compared with the other bumps. If the semiconductor device is bonded onto a circuit substrate, the reteated bumps become vertically elongated compared with the other bumps. Thus, each of the retreated bumps is optimized into a shape resistive against the propagation of destruction. Hence, the bumps disposed in the peripheral portion of the semiconductor device where they are apt to suffer a large load are improved in connection strength, so that the lifetime of bonding of the semiconductor device is elongated more greatly. Thus, the second object is achieved. In addition, the formation of bumps on the inclined portion of the thick-film electrically insulating layer can cope with miniaturization of the semiconductor device. Incidentally, in this specification, the thick-film electrically insulating layer is referred to as xe2x80x9cstress relaxation layerxe2x80x9d.